An FCC study has found that one in six U.S. mobile phone users have experienced what is being termed as “bill shock”. Bill shock is defined by the FCC as a mobile phone customer who finds a sudden increase in their mobile phone bill without any change to their service plan. The one in six number translates to approximately 30 million Americans.

Sudden increases outside of a change in service plan could occur as a result of a consumer exceeding their limits on minutes of use, text messages, or data downloads. When it came to charges as a result of exceeding limits, 84% of those surveyed said that they were not contacted by their carrier when they were about to exceed their limits. 88% said they were not contacted by their carrier even after the sudden bill increase.

Of those who have experienced bill shock, 36% saw their bill go up between $1 to $24. The next largest segment were bill increases of over $100 at 23%. Bill increases of $25-$49, $50-$74 and $75-$99 were experienced by 15%, 10% and 4% respectively. 12% did not know how much their bill increased.

The survey, conducted between April and May this year included 3,005 U.S. adults.